Rapid prototyped transfer tray for orthodontic appliances

ABSTRACT

The present invention is directed to computer-implemented methods of making a transfer tray using rapid prototyping techniques, where the gingival edge of the tray is defined to intersect with at least one receptacle for receiving an orthodontic appliance. This tray configuration helps to minimize the travel distance of the tray when placing the tray over a patient&#39;s teeth, while also preserving a high degree of mechanical retention for retaining the appliance until such time that the appliance is bonded to the tooth. Other aspects of the tray and associated methods of bonding are directed to a frangible web that extends over the gingival portion of the receptacle and fractures to facilitate tray removal after bonding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/261,281,filed Sep. 9, 2016, which is a continuation of U.S. application Ser. No.14/820,032, filed Aug. 6, 2015, which is a continuation of U.S.application Ser. No. 12/997,663, filed Dec. 13, 2010, abandoned, whichis a national stage filing under 35 U.S.C. 371 of PCT/US2009/047430,filed Jun. 16, 2009, which claims priority to U.S. ProvisionalApplication No. 61/075,831, filed Jun. 26, 2008, the disclosures ofwhich are incorporated by reference in their entireties herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to transfer trays that are used by orthodontictreating professionals to bond appliances to the teeth of an orthodonticpatient. The invention is also related to methods for making suchtransfer trays.

2. Description of the Related Art

Orthodontics is the area and specialty of dentistry associated with thesupervision, guidance and correction of malpositioned teeth to desiredlocations in the oral cavity. Orthodontic treatment can improve thepatient's facial appearance, especially in instances where the teeth arenoticeably crooked or where the upper and lower teeth are out ofalignment with each other. Orthodontic treatment can also enhance thefunction of the teeth by providing better occlusion during mastication.

One common type of orthodontic treatment involves the use of tiny,slotted appliances known as brackets. The brackets are fixed to thepatient's teeth and a resilient, generally U-shaped archwire is placedin the slot of each bracket. As the teeth are crooked, the archwire isdeflected from its original shape as it is placed in the slot of eachbracket. During treatment, the archwire gradually springs back to itsoriginal shape and, in so doing, urges the teeth to the desiredlocations.

The ends of orthodontic archwires are often connected to smallappliances known as buccal tubes that are, in turn, secured to thepatient's molar teeth. In many instances, a set of brackets, buccaltubes and an archwire is provided for each of the patient's upper andlower dental arches. The combination of brackets, buccal tubes andarchwires is commonly referred to as “braces”.

In many types of orthodontic techniques, the precise position of theappliances on the teeth is an important factor in predicting the finalteeth positions. One common type of orthodontic technique is known asthe “straight-wire” method, introduced by Dr. L. F. Andrews in 1972. Inthe “straight-wire” method, the set of appliances is configured suchthat the archwire lies in a horizontal plane at the conclusion oftreatment. Consequently, the appliances must be correctly positioned atthe beginning of treatment so that the teeth are properly aligned oncethe archwire straightens and lies in the horizontal plane. If, forexample, a bracket is attached to the tooth at a location that is tooclose to the occlusal or outer tip of the tooth, the orthodontist usinga straight-wire technique will likely find that the tooth in its finalposition is unduly intruded. On the other hand, if the bracket isattached to the tooth at a location closer to the gingiva than isappropriate, it is likely that the final position of the tooth will bemore extruded than desired.

One technique for bonding orthodontic appliances to teeth is known as anindirect bonding technique. In the past, known indirect bondingtechniques have often used a placement device or transfer apparatushaving a shape that matches a configuration of at least a portion of thepatient's dental arch. One type of transfer apparatus is called a“transfer tray” or “indirect bonding tray”, and typically has anelongated cavity for simultaneously receiving a number of teeth. A setof appliances such as brackets is releasably connected to the innersurface of the tray at certain, predetermined locations.

During the use of a bonding tray for indirect bonding, an adhesive istypically applied to the base of each appliance by the orthodontist or astaff member. The tray is then placed over the patient's teeth andremains in place until such time as the adhesive hardens. Next, the trayis detached from the teeth as well as from the appliances, with theresult that all of the appliances previously connected to the tray arenow bonded to respective teeth at their intended, predeterminedlocations.

Indirect bonding trays are normally custom-made for each patient becausethe size and orientation of teeth can vary widely from one patient tothe next. One method of making indirect bonding trays includes the stepsof taking an impression of each of the patient's dental arches and thenmaking a replica plaster or “stone” model from each impression. Ifdesired, the teeth of the model can be marked with a pencil to assist inplacing the brackets in ideal positions. Next, the brackets aretemporarily bonded to the stone models using a suitable adhesive. Anindirect bonding tray is then made by placing matrix material over themodel as well as over the brackets on the model. For example, in athermoforming method, a plastic sheet matrix material may be placed overthe model and brackets and then heated in an oven under vacuum. As theplastic sheet material softens and as air in the oven is evacuated, theplastic sheet material assumes a configuration that precisely matchesthe shape of the replica teeth of the stone model and adjacent brackets.The plastic material is then allowed to cool and harden to form a tray.As an alternative to thermoforming, it is possible to cast a suitableresin, such as silicone, around the teeth of the model and then hardenthe resin to produce the tray. In this case, a casting vessel issometimes used to contain the resin prior to hardening.

Once the tray has been formed, it is carefully detached from the stonereplica, along with the associated appliances. When the tray isdetached, the adhesive used to bond each appliance to the model istypically retained on the base of each appliance. This adhesive pad,also called the custom resin base, conforms closely with the bondingsurface on the replica tooth. Finally, the transfer tray is cleaned andtrimmed as may be desired to provide a proper fit in the mouth.

While the state of the art with respect to indirect bonding trays hasadvanced in recent years, there is a continuing need to improve the easeof making and using such bonding trays.

SUMMARY OF THE INVENTION

The preparation of transfer trays can be, unfortunately, both laboriousand time-consuming for the treating professional or lab technician. Theconventional process of either thermoforming or casting the trayrequires the intervention of an operator and is subject to human error,particularly in the manual positioning of brackets on the model.Moreover, the steps of preparing a replica dental model, bondingappliances to the replica model, detaching the tray from the model, andeventually cleaning and trimming of the finished tray, each incuradditional time or materials costs.

The present invention is directed in one aspect to a method of making acustomized transfer tray for bonding orthodontic appliances to the teethof an orthodontic patient. The tray is configured in the virtual worldby defining the desired location of each orthodontic appliance andconfiguring a virtual transfer tray that fits over the teeth andincludes a plurality of appliance receptacles that precisely locate eachappliance in its respective desired location. The method furtherincludes defining a gingival edge of the transfer tray such that theedge intersects each receptacle. A physical transfer tray is then formedusing rapid prototyping techniques based on the exact configuration ofthe virtual transfer tray configured therefrom.

By configuring the gingival edge of the transfer tray to intersect eachreceptacle, the treating professional gains particular advantages duringthe bonding procedure. First, the transfer tray only partiallyencapsulates each appliance, thereby facilitating both engagement anddisengagement of the transfer tray from appliances. Second, positioningthe receptacles at the gingival edge of the transfer tray also reducesthe travel distance of the tray during seating, thereby minimizingadhesive smearing during the bonding (particularly when using two-partchemical cure adhesives). This transfer tray may be pre-loaded withorthodontic appliances by the manufacturer or alternatively may beloaded by the treating professional prior to bonding. By automating thetray manufacturing based directly on digital data, this method alsooffers improved product consistency, compared with manually preparedtransfer trays.

The transfer tray may also include a thin frangible web of material thatpartially extends across gingival portions of the appliance, such thatthe appliance is securely retained in the tray prior to bonding. Oncethe appliance has been bonded to the patient's dental structure, thefrangible web can then be fractured and the tray removed from thepatient's mouth by urging the transfer tray in the occlusal direction.The presence of a frangible web is particularly advantageous since itprovides both convenient loading and retention of the appliance into thetray, as well as easy detachment of the tray from the patient's dentalstructure. Detachment of the tray in the occlusal direction isconvenient and comfortable for the patient since it does not involvepulling the tray outward against the cheeks or lips. Occlusal trayremoval is also helps minimize the risk of accidentally debonding thenewly bonded appliances, since it avoids the need to pull the appliancesaway from the tooth surface in the labial direction (or lingualdirection in the case of lingual appliances).

The use of rapid prototyping techniques to fabricate the transfer trayis advantageous because it provides the freedom for the receptaclegeometry to be adapted for easy engagement and disengagement of theorthodontic appliance from the tray. Other known fabrication methods,such as casting and thermoforming, fully surround the appliance with amatrix material to form the shape of the receptacle. While this iseffective in retaining the appliance, this configuration is alsoinherently disadvantageous since the strong mechanical retention of theappliance can result in detaching the appliances from the teeth as thetray is removed from the mouth. The risk of bond failures is oftentimesso significant that the treating professional or assistant is compelledto manually section the tray into several pieces to facilitate removingthe tray from the mouth, which is a nuisance. The present inventionprovides both a high level of mechanical retention for precisepositioning of the appliance prior to bonding, as well as rapid and easydisengagement of the tray from the mouth in one piece after bonding.

Other aspects of the tray derive from incorporating multiple materials,or components, into the transfer tray. Using two or more components isbeneficial because each part of the tray has its own set of materialrequirements based on its particular function. For example, the transfertray may include one or more stop members that specifically engagepredetermined portions of occlusal teeth surfaces during a bondingprocedure. By forming stop member(s) from a material that is harder thanthe rest of the tray, it is possible to form a “positive hard stop”between the tray and the teeth, thereby providing increased accuracy inpositioning each appliance on its respective tooth surface. As anotherexample, the transfer tray may further include one or more receptaclesthat are formulated from relatively softer materials to facilitaterelease of appliances from the tray when detaching the transfer trayfrom the patient's teeth after bonding.

As a further advantage, rapid prototyping techniques provide greaterfreedom to construct components of the transfer tray independently ofeach other. These configurations may include spatial arrangements ofstop members and/or receptacles that are difficult or impossible tofabricate using traditional thermoforming or casting methods. Forexample, transfer trays that are thermoformed or cast generally displayat least one single continuous layer that extends across the entiretray. This need not be the case with trays formed by rapid prototyping,which may include, for example, patterned layers.

In another aspect, the present invention is directed to a method ofmaking a transfer tray for indirect bonding an orthodontic applianceincluding obtaining a virtual model of a patient's dental structure,determining a desired location for a virtual orthodontic appliance onthe model, placing a virtual appliance receptacle at the desiredlocation, where the virtual receptacle has a configuration that matchesat least a portion of the appliance, deriving a virtual tray bodyextending across at least a portion of the model and at least a portionof the receptacle remote from the model, where the act of deriving avirtual tray body includes the act of defining a gingival edge of thetray body that intersects the virtual receptacle, forming the transfertray by rapid prototyping, where the transfer tray includes a physicaltray body and a physical receptacle that correspond to the virtual traybody and virtual receptacle respectively.

In still another aspect, the invention is directed to a method ofbonding an orthodontic appliance to a patient's dental structure,including obtaining a virtual model of a patient's dental structure,determining a desired location for a virtual orthodontic appliance onthe model, placing a virtual appliance receptacle at the desiredlocation, where the virtual receptacle has a configuration that matchesat least a portion of the appliance, deriving a virtual tray bodyextending across at least a portion of the model and at least a portionof the receptacle remote from the model, where the act of deriving avirtual tray body includes the act of defining an gingival edge of thetray body that intersects the virtual receptacle. The method furtherincludes forming the transfer tray by rapid prototyping, where thetransfer tray includes a physical tray body and a physical receptaclethat correspond to the virtual tray body and virtual receptaclerespectively, placing the appliance in the physical receptacle, applyingan adhesive to the surface of the orthodontic appliance, placing thetransfer tray over the patient's dental structure, and hardening theadhesive.

In yet another aspect, the invention is directed to a method of bondingan orthodontic appliance to a patient's dental structure includingproviding an orthodontic transfer tray having a receptacle and anorthodontic appliance received in the receptacle, placing the transfertray over the patient's dental structure, bonding the appliance to thepatient's dental structure with an adhesive, and subsequently detachingthe transfer tray from the appliance by urging the transfer tray in agenerally occlusal direction, wherein the act of detaching the transfertray includes fracturing a portion of the tray that extends across atleast a portion of a gingival side of the receptacle.

DEFINITIONS

As used herein:

“Mesial” means in a direction toward the center of the patient's curveddental arch.“Distal” means in a direction away from the center of the patient'scurved dental arch.“Occlusal” means in a direction toward the outer tips of the patient'steeth.“Gingival” means in a direction toward the patient's gums or gingiva.“Facial” means in a direction toward the patient's lips or cheeks.“Lingual” means in a direction toward the patient's tongue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a method of making a physicaltransfer tray according to one embodiment of the invention.

FIG. 2 is a perspective view of an exemplary virtual dental model.

FIG. 3 is a perspective view of a composite model including virtualorthodontic appliances mounted on the model of FIG. 2.

FIG. 4 is a perspective view showing the process of defining a virtualstop member that engages the composite model of FIG. 3.

FIG. 5 is a perspective view showing the stop member of FIG. 4 in itsfinished configuration.

FIG. 6 shows the process of deriving a virtual outer surface over thecomposite model and stop member of FIG. 5.

FIG. 7 is a perspective view showing the finished outer surfaceextending over the model and appliances of FIG. 5.

FIG. 8 is an inverted perspective view showing the outer shape of avirtual object that is derived from the finished outer surface of FIG.7, illustrating gingival and facial sides.

FIG. 9 is a perspective view of a virtual transfer tray precursor formedby subtracting the model and appliances of FIG. 3 from the outer shapeof FIG. 8.

FIG. 10 is a gingival view of a virtual raw tray assembly formed bymerging the tray precursor of FIG. 9 and stop member of FIG. 5.

FIG. 11 is a gingival view of a virtual transfer tray formed by defininga cutting surface and virtually removing portions of the raw trayassembly of FIG. 10 located gingival to the cutting surface.

FIG. 11a is a lingual view of the tray in FIG. 11, with virtualappliances in place.

FIG. 12 is a gingival view of a physical transfer tray corresponding tothe virtual transfer tray of FIGS. 11 and 11 a, with physical appliancesin place.

FIG. 13 is a close up view of a physical appliance placed in thephysical transfer tray of FIG. 12, taken from the portion designated“13” in FIG. 12.

FIG. 14 is a side cross-sectional view of the tray illustrated in FIG.13 after the tray has been detached from the dental arch model andtrimmed, and further depicting the tray as it might appear immediatelybefore placing the tray over the patient's dental structure.

FIG. 15 is a gingival view of a physical transfer tray according toanother embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, a “virtual” object includes digital data thatrepresents, defines or renders a viewable 3D model of the object, or themodel itself. In the examples below, the concepts of a “virtual object”,“virtual model” and “digital image” are used interchangeably. Virtualobjects can be stored, processed, and/or communicated using a backoffice server or workstation, such as a general purpose computer havinga processor capable of manipulating digital images, a user interface,and a display to allow a user to view digital images. The computerfurther includes memory that is capable of storing multiple sets ofvirtual models and fully accessible to software running on the computer.The rapid prototyping machine and computer are typically located in thesame place, but this need not be the case. Since digital information canbe transferred over a wired data connection or the Internet, datarepresenting a patient's dental structure may be acquired andmanipulated in the office of the treating professional, and the transfertray itself manufactured using an off-site rapid prototyping machine.

FIG. 1 is a schematic block diagram describing a workflow used to make atransfer tray for placing orthodontic appliances on a patient's teethaccording to exemplary embodiments of the present invention. The firstblock, designated by the numeral 100, represents the step of providing avirtual model of a patient's dental structure. FIG. 2 shows a virtualmodel 10 derived in block 100 as might be seen on a computer display. Asshown, the model 10 represents the inverted upper arch of a patient andincludes a plurality of teeth 12. In more detail, the teeth 12 includeleft and right central teeth 11, lateral teeth 14, cuspid teeth 15,bicuspid teeth 18, and first molar teeth 19, as well as surroundinggingival tissues 13. In this particular dental arch, there are twobicuspid teeth 18 on the left side but only a single biscuspid tooth 18on the right side.

Model 10 can be obtained using digital data provided using a hand-heldintra-oral scanner such as the intra-oral scanner using active wavefrontsampling developed by Brontes Technologies, Inc. (Lexington, Mass.).Alternatively, other intra-oral scanners or intra-oral contact probesmay be used. As another option, the digital data may be obtained byscanning an impression or other negative replica of the patient's dentalstructure. As still another option, the model 10 may be obtained byscanning a positive replica of the dental structure or by using acontact probe on the positive replica. The positive replica used forscanning may be made by pouring a casting material (such as plaster ofParis or epoxy resin) into an impression of the patient's teeth andallowing the casting material to cure. If scanning is used, any suitablescanning technique may then be used to obtain the model 10, includingX-ray scanning, laser scanning, computed tomography (CT), and magneticresonance imaging.

Additional steps may be used to further refine the digital data beforerendering the model. For example, the digital data representing model 10may be additionally filtered or processed by removing erroneous datapoints. For example, STL (stereolithography) data files representing atooth surface that include a data point significantly outside the normalexpected geometrical relationship of adjacent data points could be fixedby STL-handling software to remove the erroneous data point. Inaddition, tooth data points that are missing could be added by softwarethat manipulates STL files to create realistic, smoothly curved toothshapes. In some embodiments, data processing is carried out beforeconversion of the data to an STL file.

The workflow then proceeds to block 102, where one or more virtualappliances are placed at desired locations on the teeth 12 of model 10to form a composite model. This composite model is illustrated in FIG. 3and shows virtual orthodontic appliances 16 connected to the virtualcentral teeth 11, lateral teeth 14, cuspid teeth 15, and bicuspid teeth18 of the model 10. Although not shown here, one or more bondable molarappliances can optionally be connected to the virtual molar teeth 19 ofthe model 10. In the present embodiment, the appliances 16 arerepresented by labial brackets. However, appliances 16 may also includelingual brackets, molar tubes, buttons, cleats, sheaths, or any otherorthodontic appliances suitable for bonding to the surfaces of teeth. Insome embodiments, the appliances 16 are directly provided in the form ofan STL file, or other digital image, by the appliance manufacturer.Alternatively, the digital images representing the appliances 16 mayprovided by scanning the physical appliance, or appliances, themselves.Preferably, the appliances 16 are exact virtual replicas of the physicalappliances to be bonded to the teeth of the patient.

As shown, each appliance 16 includes a virtual base 17 which in turn hasa tooth-facing surface that contacts a respective tooth 12 when theappliance 16 is positioned in its desired location. Each appliance 16may be a based on a standardized “off-the-shelf” bracket or,alternatively, may be custom made according to the unique dentalstructure of the patient.

In the latter case, the base 17 of each appliance 16 preferably includesa tooth-facing surface contour that exactly matches that of itsrespective tooth 12 when the appliance is in its desired location.Examples of customized orthodontic appliances in the art include U.S.Pat. No. 6,776,614 (Weichmann et al.), RE35,169 (Lemchen et al.), U.S.Pat. No. 5,447,432 (Andreiko et al.), U.S. Pat. No. 5,431,562 (Andreikoet al.), and U.S. Pat. No. 5,454,717 (Andreiko et al.).

The desired locations for the appliances 16 on the model 10 can bedetermined in any of a number of ways. In one example, the treatingprofessional manually selects and places the virtual appliances 16directly on the model 10 using the local computer. In some embodiments,the modeling software treats each appliance 16 and each tooth 12 as aseparate object within the 3D environment and fixes the position of eachappliance 16 within the 3D space relative to a coordinate systemassociated with the tooth 12 of the corresponding appliance 16. Themodeling software can then, for example, virtually connect theappliances 16 to a virtual archwire selected by the practitioner andcompute the final positions of the teeth 12 based on the positions ofthe appliances 16 and the selected archwire. The modeling software canthen display the virtual teeth 12 in their final occlusion for review bythe treating professional.

If the treating professional is not entirely satisfied with the finalpredicted positions of the teeth, the treating professional may use themodeling software to manipulate one or more of the virtual appliances 16relative to the teeth 12. Based on these adjustments, the modelingsoftware can again virtually connect the appliances 16 to the virtualarchwire, for example, to simulate the movement of teeth to new finalpositions. The new final positions of the teeth 12, determined by thepositions of corresponding appliances 16, are then computed anddisplayed for review. These steps can be repeated as many times asdesired until the treating professional is satisfied with the finalpositions of the teeth 12 as represented by the modeling software. As analternative to moving appliances, the treating professional may insteaduse the modeling software to define the desired positions of teeth 12,and have the modeling software determine the suitable locations to placethe appliances 16 in order to move the teeth 12 to those desiredpositions. Examples of virtual orthodontic treatment are disclosed inissued U.S. Pat. No. 6,739,869 (Kopelman et al.), U.S. Pat. No.7,354,268 (Raby et al.) and published U.S. Patent Application No.2008/0096151 (Cinader, Jr. et al.).

As another option, the steps in block 102 may be carried out by atechnician at a location remote from the treating professional's office.For example, a technician at the appliance manufacturer's facility mayuse the modeling software to place appliances 16 on the model 10 basedon standards or guidelines from an orthodontic treatment philosophy,such as for example that of Drs. MacLaughlin, Bennett, and Trevisi.These standards or guidelines for appliance placement may be specific toeach tooth 12 in model 10, and call out the position of the archwireslot (an occlusal-gingival height, for example) with respect to theclinical crown of each tooth 12. The technician may also placeappliances 16 in accordance with particular instructions provided by thetreating professional. Once the technician is satisfied with theappliance positions and the resulting finished positions of the teeth,the model 10, together with the data representing the positions ofappliances 16, are transmitted to the treating professional for review.The treating professional can then either approve the technician'sappliance placement positions or reposition the appliances 16 asdesired.

As yet another option, the local computer can automatically suggestlocations of appliances 16 on the teeth 12 to the treating professional.Again, these proposed appliance locations are optionally based upon anorthodontic treatment philosophy or other known standards or guidelinesin the art. Examples of automatically placing virtual brackets on teethare described in issued U.S. Pat. No. 7,210,929 (Raby, et al.) andpublished U.S. Patent Application Nos. 2006/0024637 (Raby, et al.) and2007/0238064 (Raby, et al.). As before, the treating professional hasthe opportunity to review the computer-proposed locations of appliances16 and can either approve the placement positions or reposition theappliances 16 as desired.

As indicated in block 104 and further illustrated in FIGS. 4 and 5, thelocal computer then derives a stop member 32 (FIG. 5) that virtuallyengages the teeth 12. This process proceeds as shown in FIG. 4 bydefining a first generally oval-shaped surface 20 extending over theupper left first molar tooth 19, a second generally oval-shaped surface22 extending over the upper right first molar tooth 19, and a thirdelongated surface 24 extending over the two upper central incisor teeth11. The first, second, and third surfaces 20,22,24 may alternativelyassume generally square, circular, or irregular shapes, if desired.Moreover, the surfaces 20,22,24 can be defined using a manual process,automatic process, or combination thereof. In a manual process, eachsurface 20,22,24 may be drawn by a technician, for example, using amouse or other pointing device. In an automatic process, surfaces20,22,24 may be defined by a software subroutine that isolates a giventooth object, projects the tooth object onto an occlusal plane of themodel 10 to define a 2D surface, and then optionally scales the surfaceto extend across some or all of the occlusal surfaces of the toothobject.

The surfaces 20,22,24 are then aligned with the occlusal surfaces oftheir corresponding teeth 12, and virtually extruded towards thegingival direction until each surface 20,22,24 at least partiallyoverlaps the crown(s) of the respective teeth 12. As shown, the surfaces20,22,24 overlap to some degree with the underlying teeth 12 but stopshort of overlapping any of the appliances 16. The extrusion of thesurface 20, surface 22, and surface 24 sweeps out, in 3D space, firstvolume 26, second volume 28, and third volume 30, respectively. Once thefirst, second, and third volumes 26,28,30 have been defined, the model10 is then virtually subtracted from each to produce respectiveposterior sections 27,29 and anterior section 31 as shown in FIG. 5. Theposterior sections 27,29 and the anterior section 31 therefore havesurface contours complemental to the occlusal surface contours of therespective underlying teeth 12. Optionally and as shown, a generallyU-shaped flexible section 34 is additionally defined, which connects theposterior sections 27,29 and anterior section 31 to each other to formthe integral stop member 32. The inclusion of the flexible section 34advantageously registers the sections 27,29,31 with respect to eachother in 3D space. The particular geometry of flexible section 34furthermore provides particular advantages in the finished transfertray, which shall be discussed later.

Next, block 106, along with FIGS. 6 and 7, illustrate the derivation ofan outer surface that extends over both the model 10 and the stop member32. In this embodiment, the derivation proceeds by defining a guidanceline 40 that extends across at least a portion of the arch and is spacedaway from the model 10 and mounted appliances 16. In the example shown,the guidance line 40 follows a curved path that is generally parallel tothe facial surfaces of the appliances 16 and generally lies in anocclusal plane. However, one or more guidance lines 40 may also bedefined which traverse the occlusal or lingual surfaces of the arch. Inone computer-assisted embodiment, the guidance lines 40 are defined bytracing a line segment that connects the facial-most edges of appliances16 as viewed from the occlusal direction, offsetting the line segmentoutwardly towards the facial direction by a certain distance and thenapplying a smoothing operation to the line segment. If desired, thecertain distance can be used to define a desired tray thickness. Theprocess in block 106 continues by defining a series of fitted arcs 46,each of which extends over the lingual, occlusal, and facial surfaces ofthe model 10 and intersects each guidance line 40 in a generallyperpendicular relationship such that each fitted arc 46 passes over,without contacting, the model 10, mounted appliances 16, and stop member32. In this example, each fitted arc 46 is generally semi-circular inshape and begins at a location lingual relative to the teeth 12 andterminates at a location facial to the teeth 12.

FIG. 7 shows the derivation of the outer surface 50 from the fitted arcs46. The outer surface 50 represents the exterior surface of the transfertray and may be formed by fitting a surface to the set of fitted arcs46. In some embodiments, the outer surface 50 is an open-ended shellthat completely covers the occlusal, lingual, and facial sides of theassembly that includes the model 10, appliances 16, and stop member 32.Optionally, a surface smoothing operation is subsequently executed onthe outer surface 50. Then, in block 108, a virtual tray body is derivedusing the outer surface 50. FIG. 8 shows the solid virtual tray body 56formed by defining a composite surface that includes the outer surface50 and a planar surface that extends across the cavity formed by theouter surface 50. When virtually aligned with the model 10, the traybody 56 surrounds both the teeth 12 and mounted appliances 16.

Next, block 110 shows the virtual subtraction of the model 10, alongwith mounted appliances 16, from the tray body 56 to produce a virtualtray precursor 60, which is shown in FIG. 9. Tray precursor 60 includesthe tray body 56, which now has a shell-like configuration and furtherincludes receptacles 62, formed by the negative virtual imprints of theappliances 16. As used herein, the term “receptacle” refers to a surfacehaving a configuration that is sufficient to releasably retain anappliance. In some embodiments, the receptacle is at least partiallycomplemental to the exterior surface of the appliance. Preferably, eachreceptacle 62 in the tray precursor 60 has a configuration that matchesat least a portion of its respective appliance 16, allowing for preciseand controlled securement between the resultant physical transfer trayand the physical appliances. If a tighter securement is desired betweenthe physical transfer tray and the physical appliances, the receptacles62 may optionally be scaled slightly smaller in one or more dimensionsto provide an interference fit with the respective appliances 16. It isnoted that this is possible because the physical tray can be fabricatedusing pliable materials that can slightly compress and/or expand toaccommodate the physical appliances in the physical receptacles.

Optionally and as shown, a midline marker 52 is added to the trayprecursor 60 to identify the location of the midline dividing the leftand right quadrants of the teeth 12 in model 10. The midline marker 52may be a raised ridge (as shown), bump, notch, groove, or any othervisually prominent feature that corresponds to the midline position ofthe teeth 12. The corresponding physical marker can later assist thetreating professional by providing visual indicator for aligning thefinished physical transfer tray while placing the tray over thepatient's dental structure.

Continuing with block 112, and as further illustrated in FIG. 10, thesubset of data representing the stop member 32 is then subtracted fromthe data set representing the tray precursor 60, and the two resultingsubsets finally merged back together to form the virtual tray assembly70. The completion of this step results in a tray assembly 70 having apartially embedded stop member 32. It is noted from the figure that someocclusal surface regions of the stop member 32 are exposed when viewingthe tray assembly 70 from the occlusal direction, and these are denotedas striped regions in this figure and in subsequent FIGS. 11, 11 a, 12,and 15. When the tray assembly 70 is virtually engaged to model 10, theexposed portions of the stop member 32 precisely register with theocclusal surfaces of the molar teeth 19 and central teeth 11 in themanner shown in FIGS. 5-6.

In block 114, a finished virtual transfer tray 80 is produced bytrimming the tray assembly 70 to create a gingival edge 79 thatintersects with one or more of the receptacles 62. This may beaccomplished by defining a virtual cutting surface that intersects withone or more of the receptacles 62 and virtually removing a portion ofthe tray body 56 that is located in the gingival direction from thecutting surface. The virtual cutting surface, and the resulting gingivaledge 79, generally extend in an occlusal plane, but rise and fall incorrespondence with the occlusal-gingival position of each receptacle.FIG. 11 shows a gingival view of the transfer tray 80 after completionof the above cutting operation. As shown, the gingival edge 79intersects each receptacle 62 in tray body 56.

FIG. 11a shows a facial view of the transfer tray 80, with virtualappliances 16 in place. From this view, it is observed that transfertray 80 has a configuration in which the gingival edge 79 generallyrises and falls based on the occlusal-gingival positions of appliances16 along the dental arch. In some embodiments, the gingival edge 79generally rises and falls based on the occlusal-gingival positions ofthree or more appliances 16 along the dental arch. Optionally and asshown, each receptacle 62 has a configuration that extends across atleast some of the facially-oriented surfaces of its respective appliance16. When the tray 80 is virtually engaged to the model 10, the tray body56 therefore extends across at least a portion of the model 10 and atleast a portion of each receptacle 62 remote from the model 10.

This configuration of tray 80 provides numerous advantages that arerealized in the resultant physical transfer tray. First, it helpsminimize the distance traveled by the resultant physical transfer trayover the patient's teeth during tray engagement. Minimizing this traveldistance, in turn, helps minimize the potential to smear, or otherwiseinterfere with, adhesives applied to the teeth during bonding. Thissituation may be encountered, for example, when using a two-component(or AB type) chemical cure adhesive where one adhesive component isapplied to the appliance and the other component is applied to thetooth. By reducing the surface area of the tray 80 located in thegingival direction from the appliances 16, less adhesive smearing canpotentially occur on the tooth side when sliding the resultant physicaltransfer tray onto the patient's teeth from the occlusal direction. Itis generally desirable to reduce the degree of adhesive smearing, sincesmearing can deplete the amount of adhesive at the bonding site andthereby decrease bond reliability.

Second, trimming the tray 80 in the manner described above helps tominimize undue contact between the resultant physical transfer tray andthe patient's gingiva. Contact between the physical transfer tray andgingiva is preferably avoided because it is unnecessary and introducesthe risk of a mismatch between the gingival tissue and the tray, whichcan interfere with proper tray seating. Further, the gingiva is apotential source of moisture in the patient's oral cavity. If moistureis present on these surfaces, contact between the gingiva and thephysical transfer tray can result in seepage of saliva into the bondingsite, which can again result in decreased bond reliability.

It is noted that the above steps in blocks 102,104,106,108,110,112,114represent just one possible sequence of steps used to produce thefinished virtual transfer tray. Further steps or substitutions of theabove steps may be used to accomplish the same result. Moreover, thesteps described need not be executed in the exact order shown above. Forexample, the step of deriving of the stop members 32 in block 104 may beperformed either before or after the step of deriving the outer surface50 in block 106 if so desired.

Block 116 and FIG. 12 show the fabrication of a physical transfer tray80′ from the virtual transfer tray 80 using rapid prototypingtechniques. As used herein, “rapid prototyping” is a process that takesvirtual designs from computer aided design (CAD) or other modelingsoftware, transforms them into a series of thin, virtual, horizontalcross-sections and then re-constructs each cross-section in physicalspace, one after the next until the model is finished. For example, arapid prototyping machine may read in data from a CAD drawing and laydown successive layers of liquid, powder, or sheet material, in order tobuild up the physical model. By automatically aligning and fusingtogether a series of cross-sections, the virtual model and physicalmodel can correspond almost identically. Advantageously, thelayer-by-layer aspect of rapid prototyping allows the creation of nearlyany shape or geometric feature. As an added benefit, rapid prototypingalso provides flexibility to fabricate articles that include two or moreinterpenetrating components with substantially different materialproperties.

Particular examples of “rapid prototyping” techniques include, but arenot limited to, three-dimensional (3D) printing, selective area laserdeposition or selective laser sintering (SLS), electrophoreticdeposition, robocasting, fused deposition modeling (FMD), laminatedobject manufacturing (LOM), stereolithography (SLA) andphotostereolithography. Issued U.S. Pat. Nos. 5,340,656, 5,490,882,5,204,055, 5,518,680, 5,490,962, 5,387,380, 5,700,289, 5,518,680, and4,672,032 describe examples of suitable rapid prototyping techniques.Particularly suitable rapid prototyping machines include the VIPER brandSLA system from 3D Systems (Rock Hill, S.C.) and EDEN brand 500V printerfrom Objet Geometries Ltd. (Rehovot, ISRAEL).

Once fabricated, the resulting physical transfer tray 80′ is ready to beloaded with one or more appliances 16′. Each appliance 16′ is manuallyor automatically placed into its respective receptacle 62′ of the tray80′ to produce the assembly shown in FIGS. 12-14. If accuratelyfabricated, the tray 80′ is an exact physical replica of the virtualtray 80. As shown, the tray 80′ includes a physical stop member 32′(along with a physical flexible section 34′), physical tray body 56′,and physical mid-line marker 52′. Preferably, the stop member 32′ andthe tray body 56′ are composed of materials that facilitate the accurateand reproducible seating of the physical transfer tray 80′ against thepatient's teeth. When fully seated against the patient's dentalstructure, the stop member 32′, along with the tray 80′, assumes aunique position and orientation with respect to the dental structure.Such control is highly advantageous in precisely positioning physicalappliances 16′ in desired locations. As the tray 80′ is urged in thegingival direction and seated against the patient's dental structure,the stop member 32′ additionally provides a clear, tactile sensationthat indicates the tray 80′ has been fully seated due to the relativelyhard nature of the stop member 32′.

As an added benefit, the stop member 32′ can also be used to tailor thestiffness and resilience of the finished transfer tray 80′. Optionallyand as shown in FIGS. 5 and 6, the cross-section of the flexible section34′ is rectangular in shape when considered in a plane perpendicular toits longitudinal axis, with an occlusal-gingival dimension greater thanits lingual-facial dimension. The aspect ratio of the flexible section34′ is advantageous because it allows the tray 80′ to be preferentiallystiffened along particular directions. In this example, the stiffness ofthe transfer tray 80′ along the longer cross-sectional dimension of theflexible section 34′ (or occlusal-gingival directions) is significantlyincreased to minimize sagging of the tray 80′ due to gravity whenengaged to the teeth. On the other hand, stiffness is increased to amuch lesser degree along the shorter cross-sectional dimension of theflexible section 34′ (or lingual-facial directions), therebyfacilitating transverse deflection of the tray. Easy deflection of thetray in the transverse directions provides the advantage of facilitatingboth engagement and disengagement of the transfer tray 80′ in the mouth.

In some embodiments, the tray body 56′ is formed from a first rapidprototyping material with a certain stiffness. Stiffness, in turn, maybe characterized using any number of methods, including Shore Ahardness, Shore D hardness, tensile stress at 20 elongation, and tensilestress at 50 percent elongation. Preferably, the tray body 56′ has atensile stress at 20 percent elongation (according to ASTM D 412) thatis in the range of about 0.4×10⁶ to about 6.5×10⁶ Pascal, morepreferably in the range of about 0.8×10⁶ to about 3.3×10⁶ Pascal andmost preferably in the range of about 1.1×10⁶ to about 1.4×10⁶ Pascal,and has a tensile stress at 50 percent elongation that is in the rangeof about 0.8×10⁶ to about 12.5×10⁶ Pascal, more preferably in the rangeof about 1.6×10⁶ to about 6.2×10⁶ Pascal and most preferably in therange of about 2.8×10⁶ to about 3.4×10⁶ Pascal. An example of a suitablematerial for the tray body 56′ has a tensile stress at 20 percentelongation of about 1.3×10⁶ Pascal and a tensile stress at 50 percentelongation of about 3.1×10⁶ Pascal.

Optionally, the stop member 32′ is formed from second rapid prototypingmaterial with a stiffness greater than the certain stiffness of the traybody 56′ material above. Preferably, the stop member 32′ has a Shore Ahardness that is greater than about 72, more preferably has a Shore Ahardness that is greater than about 90, even more preferably has a ShoreD hardness that is greater than about 60 and most preferably has a ShoreD hardness that is greater than about 75. A suitable material for thestop member 32′ may have, for example, a hardness of 72 Shore Ahardness.

Optionally, the materials used to make the stop member 32′ and tray body56′ transmit visible light to allow the appliances 16′ to be seen whenthe tray 80′ is engaged to a patient's teeth during bonding. Usingmaterials that transmit light not only assists in determining the trayis fully seated, but also allows light curable adhesives (if used) to becured by directing actinic radiation through the tray body 56′.

FIG. 14 illustrates an exemplary use of the appliance-loaded transfertray 80′ in an indirect bonding procedure. For clarity, the stepsdescribed herein are directed to bonding a single appliance 16′ to arespective tooth 12′. This method, however, may be easily extended tobond an entire set of appliances 16′ to a plurality of teeth 12′. First,the patient's teeth 12′ that are to receive the appliances 16′ areisolated using cheek retractors, tongue guards, cotton rolls, dry anglesand/or other articles as needed. The exemplary tooth 12′ is thenthoroughly dried using pressurized air from an air syringe. Etchingsolution (such as TRANSBOND XT brand etching gel from 3M UnitekCorporation) is then dabbed onto the tooth 12′ in the general area thatis to be covered by the appliance 16′, taking care to prevent theetching solution from flowing into interproximal contacts or engagingthe skin or surrounding gingiva 13′.

After the etching solution has remained on the selected tooth surfacesfor a period of approximately 15-30 seconds, the solution is rinsed awayfrom the tooth 12′ with a stream of water for 15 seconds. The patient'steeth are then dried by the application of pressurized air from an airsyringe (for example, for a time period of 30 seconds) and excess wateris removed by suction. Care should also be undertaken to ensure that thesaliva does not come into contact with the etched enamel surface. Cottonrolls or other absorbent devices are replaced as needed, again makingsure that the saliva does not contact the etched enamel. Air from theair syringe may then be applied to the tooth 12′ again to ensure thatthe tooth 12′ is thoroughly dried. Optionally, the tooth 12′ may beprimed using, for example, TRANSBOND brand Moisture Insensitive Primerby 3M Unitek Corporation (Monrovia, Calif.).

Next, a bonding adhesive is applied to the bonding pad of the appliances16′ and/or the selected areas of the patient's tooth 12′. Optionally andas shown, the bonding adhesive is a two-component adhesive. Thetwo-component adhesive may include, for example, a first component 200such as SONDHI RAPID SET brand resin A and a second component 202 suchas SONDHI RAPID SET brand resin B, both from 3M Unitek Corporation. Thefirst component 200 is applied to the tooth-facing surface of the base17′ of the appliance 16′ and the second component 202 is applied to thearea of the patient's tooth 12′ that is to receive the correspondingappliance 16′.

After the first component 200 has been applied to the bonding pad andthe second component 202 has been applied to corresponding areas of thepatient's tooth 12′, the tray 80′ is ready for seating. First, the tray80′ is oriented such that mid-line marker 52′ is visually aligned withthe shared boundary between the two central teeth 12′ (patient'smid-line). Then the tray 80′ is then urged in the gingival directioninto mating engagement with the teeth 12′. Since the inner surfaces ofthe tray body 56′ and the occlusal stop member 32′ together match theshape of the underlying tooth 12′, the appliance 16′ is simultaneouslyseated onto the tooth 12′ at the precise location corresponding to theprevious position of the virtual appliance 16 on the virtual model 10.

When the tray 80′ is constructed using the preferred materials mentionedabove, it has been observed that the tray 80′ “snaps” into place as theinner surfaces of the tray 80′ engage the teeth 12′ of the patient'sdental arch. The tray 80′ may be sufficiently stiff to press theappliances 16′ against the tooth 12′ as the adhesive cures without theapplication of external pressure. However, as an option, externalpressure may be applied to the occlusal and facial surfaces of the tray80′ until such time as the bonding adhesive has sufficiently hardened.For example, finger pressure may be used to firmly press the appliances16′ against the facial surfaces of the patient's tooth 12′.

Other examples of suitable two-component chemical curing adhesivesinclude UNITE brand adhesive and CONCISE brand adhesive, both from 3MUnitek Corporation. As an alternative, a resin-modified glass ionomercement may be employed. As yet another option, a photocurable adhesivemay be used, such as TRANSBOND XT brand adhesive or TRANSBOND LR brandadhesive, both from 3M Unitek Corporation. Other examples of suitablephotocurable adhesive materials are described in U.S. Pat. No. 7,137,812(Cleary et al.), U.S. Pat. No. 7,449,499 (Craig et al.) and U.S. Pat.No. 7,452,924 (Aasen et al.) as well as in pending U.S. PatentPublication No. 2005/0175966 (Falsafi et al.). The transfer tray 80′ mayalso be packaged with appliances that are precoated with adhesive by themanufacturer, as described in U.S. Pat. No. 7,137,812 (Cleary et al.).An alternative method for applying primer to the patient's teeth 12′ isdescribed in U.S. Pat. No. 7,168,950 (Cinader, Jr., et al.) Once thebonding adhesive has hardened, the bonding tray 80′ is carefully removedfrom the patient's dental arch.

In some embodiments, the receptacles 62′ are open-ended in a generallygingival direction to facilitate occlusal detachment of the transfertray 80′ from the appliances 16′. By adopting a configuration where thereceptacles are completely open-ended in the gingival direction, thereis minimal interference between the tray body 56′ and the appliances 16′when the tray is urged in the occlusal direction. In the embodimentshown in FIGS. 12-14, however, the virtual receptacles 62′ are partiallyopen-ended. Partially open-ended receptacles 16′ allow gingival portionsof the appliances 16′ to protrude through the gingival edge 79′ with theadded advantage of firmly retaining the appliances 16′ in the tray 80′.More particularly, tray body 56′ includes a thin frangible web 81′ thatextends along the gingival edge 79′ and is located in the gingivaldirection from the receptacles 62′. The frangible web 81′ issufficiently pliable to allow some degree of outward stretching in thegingival direction, thereby allowing appliances 16′ to be loaded intothe receptacles 62′ from the lingual direction. Preferably, thefrangible web 81′ has both sufficient strength and sufficient rigidityto retain the appliances 16′ in a precise position relative to the tray80′.

FIG. 13 shows an enlarged view of the frangible web 81′ retaining anexemplary appliance 16′ in transfer tray 80′. The appliance 16′ includestwo gingival tiewings 82′ and a base 17′ that partially protrude throughthe gingival edge 79′ of the tray 80′. In this enlarged view, it can beseen that the frangible web 81′ is formed by portions of the tray body56′ that extend between the protruding gingival tiewings 82′ and base17′. The web 81′ optionally includes lines of weakness 83′ that areindicated by dotted lines and extend between each tiewing 82′ and thebase 17′ and between the two protruding tiewings 82′. The lines ofweakness 83′ indicate locations along which the web 81′ is likely tofracture when the appliance 16′ is urged towards the gingival directionwith a sufficient amount of force. Optionally, the lines of weakness 83′may include notches, perforations, dimples, or combinations of thesewhich act to concentrate stress along these areas and facilitatefracture of the web 81′.

Once the transfer tray 80′ has been placed in a patient's mouth andappliances 16′ bonded to the patient's dental structure, the tray 80′can be removed from the teeth 12′ by urging the tray 80′ in a generallyocclusal direction and fracturing a portion of the tray 80′ that extendsacross at least a portion of a gingival side of the receptacles 62′.Preferably, this fracture occurs along one or more lines of weakness 83′on the web 81′. Fracturing the web 81′ furthermore facilitates thesubsequent disengagement of the tray 80′ from the now-bonded appliances16′ by sliding the tray 80′ in a generally occlusal direction. It isnoted that the lines of weakness 83′ shown are exemplary and it is notnecessary that the web 81′ fractures along all of these lines.Preferably, the fractured portions of the web 81′ still remain connectedto the tray body 56′ to prevent pieces of the tray 80′ from falling intothe oral cavity of the patient.

There are particular advantages to using receptacles 62′ that arepartially or fully open-ended along the gingival edge 79′. Partially orfully open-ended receptacles 62′ allow for occlusal removal of the tray80′, which is not only convenient for the treating professional but alsohelps to avoid directing tensile forces (i.e., forces in the labialdirection) to the adhesive during removal. This is advantageous sincethe tensile strength of orthodontic adhesives can be somewhat weakimmediately after curing, and so tensile forces can cause appliances 16′to be accidentally debonded from the teeth 12′. The shear strength oforthodontic adhesives, by comparison, is comparably stronger. Occlusalremoval of the tray 80′ is also more comfortable for the patient,compared with the facial removal of conventional transfer trays.

FIG. 15 illustrates an alternative transfer tray embodiment. Transfertray 90 includes a tray body 91 and stop member 93 that matches teeth 12of the dental model 10. However, tray 90 further includes a third rapidprototyping material confined within regions 95 that surround each of aplurality of appliances 16″. The third material in regions 95 has astiffness that is less than the stiffness of either the stop member 32or the tray body 56. Preferably, the material in regions 95 has atensile stress at 20 percent elongation (according to ASTM D 412) thatis in the range of about 31,000 to about 496,000 Pascal, more preferablyin the range of about 62,000 to about 248,000 Pascal and most preferablyin the range of about 112,000 to about 136,000 Pascal, and has a tensilestress at 50 percent elongation that is in the range of about 91,000 toabout 1,460,000 Pascal, more preferably in the range of about 183,000 toabout 730,000 Pascal and most preferably in the range of about 329,000to about 402,000 Pascal. An example of a suitable material in regions 95has a tensile stress at 20 percent elongation of about 124,000 Pascaland a tensile stress at 50 percent elongation of about 365,000 Pascal.

This configuration is advantageous because the softer material inregions 95 further facilitates detaching the physical appliances 94 fromthe transfer tray 90 after bonding. The flexibility of the material inthe regions 95 also reduce the chances of inadvertently detaching theappliances 94 from the patient's teeth as transfer tray 90 is disengagedfrom the patient's dental structure after bonding. Methods for renderingand configuring the tray 90 in the virtual world, manufacturing thephysical tray 90, and associated advantages, are similar to thosealready described for tray 80′ and shall not be repeated here.

Finally, in the above detailed description, the trays 80′,90 arepresented for the bonding of labial appliances to the front side ofteeth. While not explicitly shown, it is to be understood that the trays80′,90, and the methods of making them, can be easily adapted for theindirect bonding of lingual appliances.

EXAMPLE

An exemplary transfer tray was prepared using a scanned 3D virtual modelof a patient as well as the 3D solid models of an upper 5×5 set ofVICTORY SERIES brand orthodontic brackets (3M Unitek, Monrovia, Calif.)provided in STL format. A virtual model of the patient's arch wasobtained using a digital scan of an orthodontic stone impression of apatient's upper dental arch. THREE-MATIC software (Materialise Group inLeuven, Belgium) was then used to construct a virtual model of thetransfer tray. The 5×5 set of upper orthodontic brackets was virtuallybonded to the model. A three-section integral stop member was derived tomatingly engage the occlusal contours of the left first molar, rightfirst molar and the left and right central teeth. A single guidance linewas manually traced along the facial surfaces of the virtual brackets byan operator, and this guidance line was subsequently used to derive asmoothed outer surface that was offset by 3.5 millimeters in the labialdirection from the model teeth and appliances. The virtual outer surfacewas filled using an extrusion process to form the tray body, and thetray precursor was formed by performing a Boolean subtraction betweenthe model with appliances and the tray body. The integral stop memberwas then merged with the tray precursor, and a cutting surface used todefine a gingival edge of the tray intersecting the bracket receptacles.

A physical transfer tray was then formed from the virtual transfer traymodel using an EDEN 500V brand 3-Dimensional Printing System (ObjetGeometries, Ltd., Rehovot, ISRAEL) A soft, pliable “Tango Plus” FULLCUREbrand printing resin was used for the tray body, while a relatively hard“Fullcure 720” resin (also from Objet Geometries, Ltd.) was used for theocclusal stop member. After fabrication, the transfer tray was rinsed inwater to dissolve the support material and then loaded with the physicalorthodontic brackets. The finished transfer tray was observed tocomplementally engage over the stone replica model with no difficulties.

All of the patents and patent applications mentioned above are herebyexpressly incorporated into the present disclosure. The foregoinginvention has been described in some detail by way of illustration andexample for purposes of clarity and understanding. However, variousalternatives, modifications, and equivalents may be used and the abovedescription should not be taken as limiting in the scope of theinvention which is defined by the following claims and theirequivalents.

1. A method of creating a transfer tray model, the method comprising:obtaining a virtual model of a patient's dental structure and locationsfor a plurality of virtual orthodontic appliances on the model;providing a virtual receptacle at each appliance location, wherein eachvirtual receptacle has a configuration that matches at least a portionof one of the appliances; and deriving a virtual tray body extendingacross at least a portion of the model and at least a portion of eachreceptacle remote from the model, wherein the act of deriving a virtualtray body includes the act of defining an gingival edge of the tray bodythat intersects each virtual receptacle so that, when an appliance isretained in each receptacle, all facially oriented surfaces of theappliance located in an occlusal direction from the gingival edge areenclosed by a portion of the tray body extending continuously across thereceptacle and all facially oriented surfaces of the appliance locatedin a gingival direction from the gingival edge are exposed.
 2. Themethod of claim 1 and further comprising forming the transfer tray,wherein the transfer tray includes a physical tray body and physicalreceptacles that correspond to the virtual tray body and virtualreceptacles respectively.
 3. The method of claim 2, wherein the transfertray is formed by rapid prototyping.
 4. The method of claim 1, whereinthe act of defining a gingival edge comprises trimming the virtual traybody by creating a cutting surface that intersects each receptacle andvirtually removing the portion of the tray body that is located in thegingival direction from the cutting surface.
 5. The method of claim 1,wherein the step of obtaining a virtual model of a patient's dentalstructure and locations for a plurality of virtual orthodontic applianceon the model comprises determining a desired location for the virtualorthodontic appliances on the model.
 6. The method of claim 1, furthercomprising rendering a virtual stop member that connects to the traybody and matches at least a portion of the virtual model.
 7. The methodof claim 6, wherein the virtual stop member includes a posterior sectionthat matches a portion of a molar tooth and an anterior section thatmatches a portion of an anterior tooth.
 8. The method of claim 6, andfurther comprising forming the transfer tray, wherein the transfer trayincludes a physical tray body and physical receptacles that correspondto the virtual tray body and virtual receptacles respectively, andwherein the transfer tray further includes a physical stop member thatcorresponds to the virtual stop member and wherein the physical traybody has a first Shore hardness and the physical stop member has asecond Shore hardness that is greater than the first Shore hardness. 9.The method of claim 1, further comprising placing an orthodonticappliance in one of the physical receptacles.
 10. A method of making atransfer tray for bonding an orthodontic appliance comprising: obtaininga virtual model of a patient's dental structure and a plurality ofvirtual orthodontic appliances on the model; creating a virtual traybody extending across at least a portion of the model, the virtual traybody including, for each virtual appliance, a virtual receptacle havinga configuration that matches at least a portion of the correspondingvirtual appliance, wherein the tray body extends continuously across atleast a portion of each virtual receptacle remote from the model,wherein the act of creating a virtual tray body includes the act ofdefining a gingival edge of the tray body that intersects each virtualreceptacle; and forming the transfer tray by rapid prototyping, whereinthe transfer tray includes a physical tray body and one or more aphysical receptacles that correspond to the virtual tray body andvirtual receptacles respectively, each physical receptacle sufficient toreleasably retain a physical orthodontic appliance corresponding to thevirtual appliance, whereby when a physical appliance is retained in acorresponding physical receptacle, such appliance will include firstfacially oriented surface that extend below the gingival edge of thetray body and second facially oriented surfaces of the appliance thatextend an occlusal direction from the gingival edge of the tray body,wherein all the second surfaces are enclosed by the portion of the traybody extending continuously across the physical receptacle and the firstsurfaces are not enclosed by any portion of the tray body.
 11. Themethod of claim 10, wherein the physical receptacle is open-ended in agenerally gingival direction to facilitate occlusal detachment of thetransfer tray from the corresponding physical orthodontic appliance. 12.The method of claim 10, wherein the act of creating a virtual tray bodyincludes the steps of providing a virtual receptacle at each appliancelocation, wherein each virtual receptacle has a configuration thatmatches at least a portion of one of the appliances; and deriving avirtual tray body extending across at least a portion of the model andat least a portion of each receptacle remote from the model.
 13. Themethod of claim 10, wherein the act of defining a gingival edgecomprises trimming the virtual tray body by creating a cutting surfacethat intersects each receptacle and virtually removing the portion ofthe tray body that is located in the gingival direction from the cuttingsurface.
 14. The method of claim 10, wherein the step of obtaining avirtual model of a patient's dental structure and locations for aplurality of virtual orthodontic appliance on the model comprisesdetermining a desired location for the virtual orthodontic appliances onthe model.